The present invention relates to an optical waveguide including a joined assembly of a core and cladding layers and suitable for use in a light source module, an optical interconnection, an optical communication component, or the like, and an optical information processing device such as a display device or the like.
Heretofore, it has been customary to transmit information across relatively small distances between boards in electronic devices or chip surfaces on boards thereof primarily with electric signals. For better performance of integrated circuits of electronic devices, it is necessary that electric signals in those integrated circuits be transmitted faster and electric signal interconnections in those integrated circuits be constructed at higher densities. However, signal delays due to time constants of the electric signal interconnections and noise caused by the electric signal interconnections have prevented electric signals from being transmitted faster and also prevented the electric signal interconnections from being constructed at higher densities.
Attention has been directed to optical interconnections as mediums for information transmission. Optical interconnections are applicable to various locations such as between electronic devices, between boards in electronic devices, and between chips in boards, etc. For signal transmission across a short distance such as between chips, there may be constructed an optical transmission/communication system having an optical waveguide formed on a board with the chips mounted thereon, the optical waveguide serving as a transmission path for transmitting a laser beam or the like which is modulated by a signal.
It is also known that an optical waveguide is used as a light source module for display devices. For example, there has been developed a head mounted display (HMD) for the user to enjoy video software images, game images, computer images, and movie images on a large screen occupied by the user alone. As shown in FIG. 20 of the accompanying drawings, there has been proposed a personal display that the user can wear like sunglasses for viewing a virtual image anywhere at will (see U.S. Pat. No. 5,467,104).
The known head mounted display has a light source including red, green, and blue light-emitting diodes (LEDs). Light emitted by an LED is not coherent, but is radiated through a wide radiation angle, and is difficult to converge to combine three colors. There is known a technique for passing LED light in three colors through an optical waveguide for producing uniform white light (Nikkei Electronics Mar. 31, 2003, page 127).
FIGS. 21A and 21B of the accompanying drawings show a module assembly including LEDs and an optical waveguide, which has been developed by Lumileds Lighting, LLC., U.S.A. FIG. 21A is a cross-sectional view of the module assembly and FIG. 21B is a perspective view of the module assembly.
As shown in FIGS. 21A and 21B, a backlight module 80 includes three RGB LED modules 82 mounted on a printed-circuit board 81, an optical waveguide 83, two reflecting mirrors 84a, 84b, and a light guide plate 85. The LED modules 82 are mounted at spaced intervals of 9 mm in a linear array. RGB LED light 86 emitted from the LED modules 82 is mixed into substantially uniform white light by being reflected by the reflecting mirrors 84a, 84b and within the optical waveguide 83, and the white light is transmitted through the light guide plate 85 and applied to the back of a liquid crystal panel.
There is also known an optical waveguide having a core whose cross-sectional size is progressively linearly smaller from a light entrance end thereof toward a light exit end thereof, as shown in FIG. 22 of the accompanying drawings (Japanese patent Laid-open No. Hei 5-173036 (page 2, the scope of claims, and page 3, column 3, lines 3-4, and FIG. 1(d))).
The optical waveguide shown in FIG. 22 has a lower cladding layer 2, a core layer 3, and an upper cladding layer 4 indicated by the imaginary lines, which are successively mounted on a board 17. As shown in FIG. 22, the core layer 3 has a cross-sectional area which is progressively linearly smaller, in terms of width and height, from a light entrance end 18 thereof toward a light exit end 19 thereof. Light applied to the light entrance end 18 is guided substantially linearly through the core layer 3 and exits from the light exit end 19.
FIGS. 23A and 23B of the accompanying drawings also show a known trifurcated optical waveguide for emitting a beam of light. FIG. 23A is a plan view of the trifurcated optical waveguide and FIG. 23B is a cross-sectional view taken along line 23b-23b of FIG. 23A.
The trifurcated optical waveguide has a core layer forked into a red light core 26R, a green light core 26G, and a blue light core 26B which have respective light entrance ends faced respectively by a red light source 27R, a green light source 27G, and a blue light source 27B. The red light core 26R and the blue light core 26B are curved end portions joining the green light core 26G which extends straight, providing a common core 26. RGB signal light 28R, 28G, 28B guided through the red light core 26R, the green light core 26G, and the blue light core 26B is combined by the common core 26 and emitted as a beam of emitted light 29 from the exit end of the common core 26.
Another known optical waveguide is combined with a light source disposed below a core layer. FIG. 24 of the accompanying drawings shows such a known optical waveguide.
As shown in FIG. 24, a core layer 3 having a thickness of about 30 μm, for example, is sandwiched between a lower cladding layer 2 and an upper cladding layer 4, each having a thickness of 14 μm, for example. The core layer 3 has a constant width throughout its length from the light entrance end to the light exit end thereof. The optical waveguide has a light entrance end 23 slanted at 45° with respect to the horizontal plane of the optical waveguide. An LED 13 as a light source is disposed below the slanted light entrance end 23.
The backlight module 80 shown in FIGS. 21A and 21B has the mirrors 84a, 84b for coupling the light signal 86 from the LED modules 82 to the optical waveguide 83 and the light guide plate 85. Since the optical waveguide and the mirrors are different components, they need to be positionally adjusted when installed in position, and hence the productivity of the backlight module 80 is low. Furthermore, inasmuch as the LED modules 82 and the optical waveguide 83 are vertically separate from each other, the backlight module 80 is not suitable for low-profile integrated configurations. The backlight module 80 fails to convert the converged LED light into a light spot of desired diameter.
The optical waveguide shown in FIG. 22 is of a straight shape free of curved portions. However, the light source combined with the optical waveguide cannot freely be positioned, but needs to be located along the entrance end of the optical waveguide. Such a light source layout tends to cause a light entrance loss.
The optical waveguide shown in FIGS. 23A and 23B is capable of emitting light which has entered through the light entrance end from the light exit end that is positioned opposite to the light entrance end. However, since the LEDs cannot freely be positioned with respect to the optical waveguide, but are limited to the layout of a linear array installation at the light entrance end, they are liable to cause a light entrance loss. In addition, when the R signal light 28R and B signal light 28B are guided respectively by the red light core 26R and the blue light core 26B, leakage light 29a occurs from the curved portions of the red light core 26R and the blue light core 26B, as indicated by the broken lines in FIG. 23A. Therefore, the optical waveguide suffers low light collecting efficiency, and is not suitable for a high output design.
The optical waveguide shown in FIG. 24 can receive more light from the light source than the optical waveguides shown in FIGS. 22 and 23A, 23B because the light source (LED) 13 is disposed below the core layer 3 at the light entrance end. However, the signal light 14 from the LED light source 13 is applied to an area having a small width of the core layer 3. As the signal light 14 is radiated from the LED light source 13 through a wide radiation angle, the proportion of the signal light 14 which is reflected by the slanted light entrance end 23 on the core 3 is relatively small. The signal light which is applied to the slanted light entrance end 23 on the lower and upper cladding layers 2, 4 is wasted as a loss. Therefore, the light collecting efficiency of the optical waveguide shown in FIG. 24 is poor.